This project proposes the use of myocardial scintigraphy for: identification and quantification of ischemic and infarcted myocardium; predicting pump failure; and quantifying changes in dimensions of ischemic and infarcted myocardium. A dual image technique with Thallium-201 (201T1) and Technetium-99m-diphosphonate (99mTc EHDP) is proposed with the difference between the negative 201T1 image and the positive 99mTc EHDP image representing the ischemic zone. The investigators propose to study 25 infarcted dogs with 99mTc EHDP scans and 25 infarcted dogs with dual image scans. Infarcts sizeestimated by scan will be compared with quantitation obtained at autopsy (serial breadloafing technique). A study of 99mTc EHDP uptake by hypoxic myocardium in six dogs is also proposed. Dual image scans will be accomplished in 120-160 patients with suspected acute myocardial infarction (MI) and repeated in 24-36 hours.